Extending the Season for Concrete Construction and Repair — The Next Phase

The Corps of Engineers is embarking on the next phase, Phase III, of Cold Weather Admixture Systems (CWAS). CWAS is an innovative approach to conventional cold weather concreting. Since its inception several years ago, the Corps continues to develop this technology to benefit the user and change the approach to winter concreting. Chemical admixtures are routinely used to accelerate cement hydration and promote early strength gain in fresh concrete. To date, no single admixture, when used within the manufacturer's recommended dosage, is capable of preventing fresh concrete from freezing. External heating is still required to maintain a curing environment. This necessitates additional resources (time and money) and is expensive, given volatile energy prices. To fill this void, CWAS uses an `off-the-shelf' approach of suites of admixtures that, when used in combination, protect fresh concrete to an internal concrete temperature of −5°C. The cement hydrates and the concrete gains strength even when the temperature is below freezing. Phase I showed the feasibility of the CWAS approach and uncovered potential long-term durability benefits. Phase II further investigated CWAS formulations using elevated dosages of chemical admixtures. Throughout this time period, numerous field demonstrations have been conducted to introduce the CWAS approach to State Departments of Transportation and the U.S. Army. CWAS is catching on. The next phase seeks to optimize the admixture combinations tailoring the mixes to site-specific conditions based on the geometry and forecasted weather conditions. This capability makes CWAS a powerful tool providing users greater flexibility for winter concrete construction projects.